The invention relates to a bit synchronization method, in a receiver, for packets of binary pulses, having a predetermined short length carrying digital information with detectable transitions between binary states, and being received in an asynchronous manner relative to the bit clock, at a rate Fb; and in particular to such a method which includes a first step of sampling said pulse trains at the rate nFb, where n is a small even integer, a second step which consists of normalizing the samples x thus obtained, or samples f derived from the latter, into binary values 1 or 0, by comparing each sample to a predetermined threshold S.
The invention relates to any type of receiver which receives digital information from wire telephone lines or optical fibres or from a radio link. The modulation used for the coding of the bits may be a phase modulation (PSK) of the RZ or nRZ type for example, or of the FSK type with or without maintaining a continuous phase for the input signal of the receiver. Preferably, the bit synchronization method according to the invention relates to a homodyne or heterodyne radio receiver receiving, during digital transmission by means of frequency shift keying (FSK), packets (or frames) of binary pulses having a fixed predetermined short length at a bit rate Fb.
An arrangement for implementing the above method may be formed by means of software or hardware. In the first case the receiver comprises, in addition to an analog-to-digital converter, a control microprocessor and a calculation microprocessor. The hardware embodiment itself comprises an FSK signal demodulator, sampling means for sampling at the rate n.Fb and sample normalizing means.
The technical problem which is solved by the invention consists of obtaining, in the fastest way possible, by means of a digital technique, the optimal bit synchronization for short bit packets (each packet belonging to a frequency hop interval of the received signal), typically shorter than 100 bits, without the need for a preliminary sequence termed "training bit sequence" at the beginning of the packet, obtaining the optimal information (at the midpoint of the bits) for all the received bits of each packet.